This invention relates generally to the field of shot blasting and more particularly to a shot blast machine for deflashing thermoset molded plastic parts.
Many industrial parts that are made of plastic can be molded and substantially deflashed with abrasive particles that are projected at the parts. A system that uses abrasive particles thus lends itself to continuous operation and is advantageous because of its efficiency. This further eliminates manual deflashing and provides for an increased production relative to typical batch systems. The result is a higher capacity than other deflashing systems.
The machine of this invention provides a hold down assembly which cooperates with a continuous endless conveyor belt. The hold down is required for light and small parts, since the kinetic energy created by the blast stream of particles will move the parts on the belt and thereby fail to provide the correct exposure time of the parts to the particle stream for deflashing. The hold down assembly includes a wire mesh member which keeps the plastic molded parts on the conveyor while abrasive particles are propelled through the wire mesh to deflash the parts. In this manner, the present system eliminates the moving of parts and provides high production in a controlled process to thereby achieve a continuous finishing of the plastic molded parts. Furthermore, the system is ideally suited for handling larger parts that cannot be tumbled and smaller, fragile parts that are prone to breakage or nicking.
The machine of the present invention thus includes a continuous, variable speed conveyor system in conjunction with a hold down assembly to provide non-stop deflashing via a centrifugal blasting system with variable speed centrifugal blast wheels that thoroughly blast the parts. An adjustable blow off system can also be employed to remove light or medium amounts of carryout abrasive particles. A polyamid/polycarbonate blasting media is preferred as the abrasive particles since it causes virtually no surface alterations on the plastic parts while still providing sufficient mass for the deflashing process. This simple yet rugged construction of machine assures minimal and easy maintenance and repairs.
Further features and advantages of the blast machine of this invention are as follows:
A. The wire mesh member, in the form of an endless belt, is provided generally parallel to the conveyor belt and functions to hold down or press light weight parts on the conveyor belt so that the parts will not slide off the conveyor belt. PA1 B. The wire mesh belt and the conveyor belt are synchronized in their speeds of travel so that speed differences will not result in the creation of scratch marks on the plastic parts. Scratch marks can result if the parts roll or slide relative to either of the belts. PA1 C. The drive system for the hold down belt is connected to the drive system of the conveyor belt via gearboxes or chains. This assures synchronized movement of the belts. PA1 D. The wire mesh belt is made of a low density mesh so that the blast wheels can project the blast media through the wire mesh and into engagement with the parts to be deflashed on the conveyor below. PA1 E. The mesh or hold down belt is "floating". Stated otherwise, it is mounted in the machine so it can move up and down relative to the conveyor belt to thereby accommodate parts of different thicknesses.
Further objects, features and advantages of the invention will become apparent to those skilled in the art from a consideration of the following description and the appended claims, when taken in connection with the accompanying drawings.